Anaplastic lymphoma kinase (ALK) is a member of the insulin receptor subfamily of receptor tyrosine kinases (RTKs), with its encoding gene located on the short arm of chromosome 2 (1, 2), ALK was initially identified as part of an oncogenic fusion gene, NPM1-ALK (also known as NPMALK), in anaplastic large-cell non-Hodgkin's lymphomas (ALCL; 3). It is also part of the fusion gene EML4-ALK in non-small-cell lung cancer (NSCLC; 4). There are a few other ALK fusion genes, such as TMP3/4-ALK and RANBP2-ALK, in inflammatory myofibroblastic tumors (IMT; 5). The tyrosine kinase activities of these fusion ALK proteins are aberrantly activated and promote cell proliferation and survival (6, 7). ALK fusion proteins have also been shown to activate various signaling pathways, among which are the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and the Ras→Raf→MEK→extracellular signal regulated kinase (ERK)/mitogen-activated protein (MAP) kinase pathway with multiple interaction points to mediate the ALK signaling (8, 9).
Recently, ALK mutations were found in 6% to 14% of sporadic neuroblastomas (10-14). ALK mutations were also reported in familial neuroblastomas (13, 14). Moreover, genetic amplification of the ALK gene could also occur in neuroblastomas or cell lines derived from this tumor (10, 11, 13, 15). Except for occasional mutations in the juxtamembrane domain, most ALK mutations identified so far are within the tyrosine kinase domain of ALK. ALK mutations and/or copy gain were found particularly in advanced and metastatic neuroblastomas, and patients with ALK mutations had a worse prognosis (11, 12, 14). Several common ALK mutations were shown to be functional. For example, siRNA-mediated knockdown of the ALK expression in cell lines harboring ALK mutants F1174L or R1275Q caused cell apoptosis and suppression of cell proliferation (12-14). The F1174L and another mutant ALK, K1062M, were shown to display increased tyrosine kinase activity and promote cell focus formation, cell transformation, and xenograft tumorigenecity in nude mice (10). The oncogenicity of ALK F1174L and R1275Q was also shown in another study (12). Genetic copy gain of the ALK is also functionally important, as suggested by the demonstration that inhibition of ALK in neuroblastoma cell lines harboring ALK copy gain induced cell apoptosis through reduced signaling of the PI3K/Akt and MAP kinase pathways (15).
Mutations of the ALK gene have not been reported in human cancers other than neuroblastomas. As described herein, the present inventors investigated the mutation status of the ALK gene in various thyroid cancers, including well-differentiated papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC) and undifferentiated anaplastic thyroid cancer (ATC). Prompted by the finding of ALK mutations in ATC, a rapidly aggressive and deadly human cancer (16), the present inventors also examined melanoma and colon carcinoma for ALK mutation. Indeed, identifying mutations in human cancers is highly desirable because it can lead to the development of new therapeutics that target such fusion or mutant proteins, and to new diagnostics for identifying patients that have such gene mutations.